1. Field of the Invention
The present invention relates to a pressure reducing valve device for a vehicle and more particularly, to an improved reducing valve device for sensing a load of a vehicle, which controls a fluctuating range of dynamic characteristics.
2. Description of the Related Art
Various types of pressure reducing valve devices for a vehicle are known in the art. Generally, a load controlling reducing valve (hereinafter "LCRV") is utilized in a freight vehicle such as a luggage van which is loaded with goods. The LCRV is connected to a master cylinder and a wheel cylinder of a real brake so as to change a hydraulic ratio of front and rear brakes depending on the load carried on the vehicle, and is operated by an axle face for the load.
The direct result of the LCRV is to weaken the braking force of the rear brake so as to prevent the rear wheels from generating a spin phenomenon since during driving a freight vehicle with goods, when the vehicle is braked, first of all, the rear brake is locked in opposition to the front brake due to the concentration and load carried on the front brake.
As shown in FIG. 3, the conventional LCRV 31 is fixed to a bracket 33 fixed to a chassis frame 32 and is provided with an adjusting spring 34 for link moving resiliency between an axle face 35 and the bracket 33. If the carried load increases, the axle face 35 rises up to a dotted line (FIG. 3). At this time, the chassis frame 32 correspondingly moves down.
Accordingly, the valve stem 36 attached to the top portion of the adjusting spring 34 applies a force F2 to a piston 37 of the LCRV 31 (FIG. 4). As shown in FIG. 4, a sleeve 39 of the piston 37 receives a force F1 which is internally generated by the spring 34 and rises up to the side of a piston sleeve 40. A valve plate 41 disposed on top of the piston 37 operates to open a ball valve 42 of the piston sleeve 40 for inducing oil from the master cylinder. The oil operates the wheel cylinder of the rear brake through an outlet 44 in a lowered state of the oil pressure during passing through the ball valve 42, the piston sleeve and an inlet 43. Therefore, the rear brake has a time difference and a pressure difference compared with those of the front brake.
FIGS. 5(A), 5(B), 5(C) and 5(D) illustrate an actual or real braking line shown in the dotted line and an ideal braking curved line shown in the hard curved line. The ideal braking line means a brake oil pressure line. As shown in FIGS. 5(A), 5(B), 5(C) and 5(D), the hard curved line crossing with the dotted real braking line at a point is an ideal braking line (KERB) of an empty car, with the dotted real braking line at B point is an ideal braking line (GUW) of a loaded car, and the dotted real braking line at C point is an ideal braking line (O/L) of a surplus loaded (100%) car.
As shown in FIGS. 5(A), 5(B), and 5(C), upon comparing the real braking line and the ideal braking line, it shows that both lines are quite different from each other. In other words, the rear brake has a locking occurrence at a point except the points A, B and C. In order to eliminate the above problems, the LCRV is utilized with the car. However, even if at each loading state of the car, all states meet with the real braking line, the crossing points do not align with a setting value of all loaded states of the car. That is, the conventional LCRV 31 has a certain width of dynamic characteristics depending on the loaded weight such as empty, loaded and surplus loaded states, so that the conventional LCRV 31 cannot be used in a car which has various types of loading sources.
FIG. 5(D) illustrates a model of ideal braking lines PC-KERB, PC-GUW and PC-O/L which are close to the ideal braking curved line by using an LCRV 1 of the pressure reducing valve device according to the present invention. However, as shown in FIGS. 5(A), 5(B), and 5(C), the width of the PC value is very narrow when the conventional LCRV 31 is applied to a car which has various types of loading sources so that it is difficult to determine a proper value of PC-KERB, PC-GUW and PC-O/L.
The width of the PC value is to be determined by a spring ratio under the application of the LCRV and is expressed as follows: ##EQU1##
Where K is a friction load pressure and F.sub.s /A.sub.2 is a load pressure F.sub.1 of the spring 38, and K+F.sub.s /A.sub.2 is a coefficient and does not relate to the change of the PC value, (D-x) relates to the F.sub.2 value of the car load, S.sub.c is a spring ratio, S.sub.R is a spring rate, and Z is a coefficient of efficiency of the bracket 33.
As shown in the above expression, since the changing size of the PC value depends on S.sub.c .times.S.sub.R .times.Z, and if the value size of S.sub.c is changed, the width of the PC value is controlled, the best ideal braking line of the dynamic characteristics of the load sensing reducing valve 1 of the pressure reducing valve device for a vehicle is invented by the present inventor as the present invention.